The compressor section of a gas turbine engine (GTE) may include one or more turbines, which may each include multiple bladed discs dividing the compressor section into a number of compressor stages. The compressor section of a three spool turbofan jet engine, for example, may include an intermediate turbine and a high pressure turbine disposed in axial flow series. The intermediate pressure turbine is supported by a first spool, which is rotatably mounted within the GTE housing. Similarly, the high pressure turbine is supported by a second spool, which is rotatably mounted within the GTE housing and which extends through a longitudinal channel provided through the first spool. During operation of the GTE, the first and second spools, and therefore the intermediate and high pressure turbines, rotate to compress air received from an intake section of the GTE. The compressed air then flows into a combustion section of the GTE wherein the air is mixed with fuel and ignited to further drive the rotation of the spools and to produce forward thrust.
To ensure optimal operation of a GTE, it is generally desirable to minimize starting torque and/or eliminate any pressure surges that may occur within the GTE's compressor due to, for example, abrupt changes in power level. Thus, to regulate or stabilize the pressure within the GTE compressor, a bleed valve assembly may be fluidly coupled between a stage of the compressor and a plenum (e.g., a protected zone surrounding the GTE). When in an open position, the bleed valve assembly vents pressurized air to the plenum to reduce the pressure within the GTE compressor. When in a closed position, the bleed valve assembly prevents pressurized airflow to the plenum thus permitting the pressure within the GTE compressor to accumulate. The bleed valve assembly may be pneumatically controlled by an electro-pneumatic servo control valve, which is, in turn, electrically controlled by an engine controller. During operation, the engine controller may send command signals to the servo control valve to vary the pressure of a control fluid (e.g., pressurized air) supplied to the bleed valve assembly to move the bleed valve assembly between open and closed positions and, thus, to vent the GTE compressor to the plenum as needed to maintain the compressor pressure within a desired range.
Servo-controlled bleed valve assemblies of the type described above are well-suited for use in conjunction with certain GTE platforms, such as those experiencing large surge margins and power level shifts during operation. However, in other GTE platforms, passive regulation of the GTE compressor is sufficient. In this latter group of GTE platforms, the utilization of a servo-controlled bleed valve assembly and its associated hardware (e.g., servo control valve, plumbing, etc.) adds unnecessary weight, cost, and complexity to the gas turbine engine.
Accordingly, it is desirable to provide a bleed valve assembly operable in either: (i) a servo-controlled mode wherein the bleed valve assembly regulates the pressure of a GTE compressor in accordance with commands received from a servo control valve or other such external controller, or (ii) an autonomous mode wherein the bleed valve assembly regulates the pressure of a GTE compressor independently and thus eliminates the need for an external control system. Preferably, embodiments of such a bi-modal bleed valve assembly would permit a user to select between the servo-controlled mode and the autonomous mode in a relatively simple and intuitive manner. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended claims, taken in conjunction with the accompanying drawings and this Background.